Process for the purification of cadmium solutions

ABSTRACT

Process for producing cadmium solutions wherein said solution is contacted with a cation exchanger containing amino carboxylic- or imino carboxylic acid groups and wherein the ion exchanger is separated from the cadmium solution after having absorbed accompanying metals from said cadmium solution.

United States Patent Roever et al.

[ 51 Oct. 17, 1972 PROCESS FOR THE PURIFICATION OF CADMIUM SOLUTIONSInventors: Wilhelm Roever; Helmut Junghanss, both of Duisburg;Hans-Werner Kauczor, Leverkusen, both of Germany Farbenfabriken BayerAktiengesellschaft, Leverkusen, Germany- Filed: May 27,1970

Appl. No.: 41,052

Assignee:

Foreign Application Priority Data July 11, 1969 Germany ..P 19 29 661.8

US. Cl. ..423/100, 75/117, 75/118, 75/119, 75/120, 75/121, 75/101 BE,23/312 Int. Cl. ..C22b 17/04 Field of Search ..75/121, 101 BE, 101 R,120, 75/119, 118, 117; 23/50 BE, 312R Primary Examiner-G. T. OzakiAttorneyConnolly and l-lutz [57] ABSTRACT Process for producing cadmiumsolutions wherein said solution is contacted with a cation exchangercontaining amino carboxylicor imino carboxylic acid groups and whereinthe ion exchanger is separated from the cadmium solution after havingabsorbed accompanying metals from said cadmium solution.

7 Claims, No Drawings PROCESS FOR THE PURIFICATION OF CADMIUM SOLUTIONSThe present invention relates to a process for the purification ofcadmium solutions which are obtained in the wet processing of cementatesfrom zinc liquor purification, flue dust or other substances whichcontain cadmium.

in the recovery of cadmium by wet metallurgical processes, for examplefrom flue dusts, cementates from zinc liquor purification or othercadmium containing substances, the cadmium containing solution is freedfrom the accompanying metals prior to the recovery of cadmium. Theseaccompanying metals, e.g., zinc, thallium, indium, copper, nickel andcobalt, are often only contained in small quantities in the solutionsand must be removed, e.g., for the purpose of electrolytic cadmiumdeposition, by conventional processes whichgenerally consist of severalstages of cementation and precipitation followed by filtration.

It has now been found that the removal of the accompanying metals fromsolutions which contain cadmium can easily by carried out on certain ionexchangers and surprisingly even .if cadmium is present in a large excess. The process is characterized in that the cadmium containingsolution is contacted with a cation exchanger which containsaminocarboxylic acid or iminocarboxylic acid groups as the activeexchange groups, and after absorption by the cation exchanger of theaccompanying metals which are more firmly bound than cadmium, thecadmium solution is again separated from the ion exchanger and themetals absorbed by the cation exchanger are subsequently elutedtherefrom.

in these exchanger resins, which will hereinafter be referred toascomplexon resins, the internal complex cation bond varies in itsstability towards different metals.

Thus, for example, the following metals are more firmly bound thancadmium, the strength with which they are bound increasing with theirposition in the given sequence:

At the beginning of the process of charging the exchanger resin, whichis advantageously present in the form of its alkali metal or alkalineearth metal salt, the cations of all the metals contained in thesolution are absorbed. Thereafter, as the resin is contacted with thesolution, e.g., using the column process with solution flowing throughit, the cadmium ions initially absorbed on the resin are displaced bythe cations of those aecompanying metals in the cadmium solution whichform a more stable bond. Within the meaning of the invention, cadmiumsolutions are understood to mean aqueous cadmium salt solutions,preferably cadmium sulphate or cadmium chloride solutions, which containaccompanying metals as impurities. Owing to the strong tendency ofcadmium to form stable chloro complex anions, chloride solutions favorthe separation of accompanying metals according to the invention sincethe concentration of cadmium cations in the solution is reduced by thechloro complex formation.

It has surprisingly been found that by the process of the invention thecations of accompanying metals which form a stronger bond, such ascopper, nickel and indium, are preferentially absorbed by the ionexchanger, from a quantitive point of view, even when cadmium is presentin a large excess. In the method of procedure described hereinafter, theuse of the usual buffer solutions is also unnecessary.

The cadmium solution, e.g., a sulphate solution for cadmium electrolysishaving a pH of between 1.5 and 5,'preferably above 3, is passed in theconventional manner over an exchanger column.

The specific loading of the exchanger, i.e., the contact time of thecadmium solution in the column, if from 2 to 25 liters per hour perliter of resin volume, preferably from 4 to 10 liter/hour/liter. Itdepends upon the difference between the binding strength of cadmium andthat of the cations which are to be removed, and when several metals arepresent it depends upon that metal whose relative binding stabilityisleast compared with that of cadmium. The solution temperature for ionexchange is advantageously increased, preferably to from 60 to C.Purification of the liquor by filtration of the solution over theexchanger column is terminated as soon as one of the accompanying metalswhich are to be removed appears in the discharge from the column orexceeds the permissible concentrations. The first metal to be detectedin the outflow will be that which differs least from cadmium in itsbinding strength.

The cadmium solution treated in this way is free from the accompanyingmetals or at the most contains only milligram traces of the metalimpurities.

The charged exchanger contains, in addition to cadmium, a highlyincreased concentration of the accompanying metals removed from thesolution. Thedistribution ratio on the resin depends on the metalcontents, the pH, the temperature and the anions of the startingsolution.

After termination of the charging of the resin and up to the time whenthe metal impurity or impurities break through into the discharge, theresin is washed with water and is eluted by running a mineral acidthrough it. The accompanying metals are in this way obtained in the formof a highly concentrated solution.

The elution may be carried out with a dilute strong acid, the degree towhich the extraction solution is concentrated being influenced by theconcentration of, the acid and the specific charge of the exchanger. If,for example, elution is carried out with a 3N hydrochloric acid solutionat a specific charge of from 2 to 5 parts by volume per hour, the amountrequired will be from 2 to 2.5 parts by volume.

Substantial concentration of the accompanying metals in the middlefraction can be achieved by fractional sub-division of the eluate. Boththe first runs and the last fraction contain small quantities of cadmiumand the last fraction moreover has an increased acid content. This lastfraction may, if desired, be used again after the next charge for freshelution of the exchanger.

Since the ion exchangers of the process according to the inventionoperate in the weakly acid range, the NH alkali metal or alkaline earthmetal form of the resin is suitable for starting the process. The sodiumor calcium form is preferably used at the start of the exchangereaction, or in some cases the cadmium form.

The complex forming cation exchangers used for the process according tothe invention are of the type which carry ion exchange activeaminocarboxylic acid and/or imino carboxylic acid groups:: the saidcarboxylic acids may have from one to five carbon atoms. It isparticularly advantageous to use resins based on crosslinked polymers.which have been synthesised by the copolymerisation of monomers havingone or more olefinic double bonds, for example styrene of the one handand divinylbenzene on the other, with introduction of aminocarboxylicacid and/or iminodicarboxylic acid groups. The cation exchangers of thetype described preferably have iminodiacetic acid groups. If the saidresins have a foam structure, which can be produced when manufacturingthe resins, they also have excellent resistance to the continuous changefrom acid to alkali medium, with the consequent changes in volume, andto the effect of high temperatures.

The following examples serve to explain the process of the inventionwithout limiting it.

EXAMPLE l A cadmium sulphate containing 60.2 grams of cadmium per .literand also, as metal impurities, 0.21 g/l of Cu, 0.21 g/l of Ni and 0.18g/l of Co, is adjusted to pH 3.5 4.0 35 l of this solution are. filteredat a temperature of 65C. over a slim resin column containing 2% litersof the exchanger in the sodium form of imino diacetic acid groups. Thespecific loading of the exchanger is 5. l and, in the second half, 3 lof the solution per hour for each 1 of exchanger resin.

The cadmium solution discharged from the column is free from Ni and Cu.Ni starts to escape into the discharge after about l of solution haveflown through, and reaches a concentration of from 11 to 12 mg/l after35 l have passed through. The upper part of the exchanger resin showsthe colors of the complex non-ferrous metal compounds.

The cadmium liquor treated over the exchanger resin contains an averageof less than 1 mg/l of Cu and 5.5 mg/l of Ni whilst the'Co content hasbeen reduced to 75 mg/l.

After the resin column has been washed with water, elution is carriedout with 6.0 l of a 2.5 N H 80 solution at 60 C. and a specific load of3. The eluate is divided into three fractions. The first fraction of 1.0l contains from 3 to 4 grams of cadmium per liter and is free from acid.The third fraction contains small amounts of the accompanying metals andalso from 6 to 8 grams of cadmium per literand has a high acid content,and can be used again for elution. The accompanying metals which havebeen removed are collected in v.the main fraction of 3.5 l and arepresent in increased concentration compared with Cd. This fractioncontains 100 percent of the copper, 97.3 percent of the nickel, 57percent of the cobalt and 9.8 percent of the cadmium present in theoriginal solution.

EXAMPLE 2 Selective indium deposition by ion exchange on dicarboxylicacid resin in the sodium form was carried out for thepurpose of removingindium from a cadmium sulphate liquor obtained by the wet chemicalprocessing of the intermediate products of zinc recovery. The solution,containing g of cadmium per liter and 1.45 g of indium per liter isadjusted to a pH of 2 and treated at 65 to C. with a specific load ofthe exchanger column of from 2 to 3 l per hour per 1 of exchangervolume. Escape of indium into the solution discharged from the columnstarts after filtration of 20 parts by volume of solution on 1 part byvolume of resin, the indiumin the outflow being 1 mg/l. After 25 1 partsby volume of the filtrate, the indium content in the discharge from thecolumn rises to 10 mg/l.

The column is then washed with water and thereafter eluted with from '2to 3 parts by volume of 10 percent hydrochloric acid at 50 to 60 C. Theindium content in the eluate discharged reaches a maximum of 45 g/l. Thefirst 2 parts by volume of eluate for each volume of resin contain 18.1g of indium per liter 100 percent in addition to 3.1 g of cadmium per 11.2 percent of the original solution. The treated cadmium solutioncontains less than 1 mg of indium per liter.

EXAMPLE 3 A cadmium chloride solution containing 48.0 g of Cd per 1, 0.4g of Zn per 1 and 0.047 g ofln per 1 is passed over a slim column ofexchanger resin at a pH of 2.5 at a specific load of 4 parts by volumeof solution per hour. The. temperature of the solution is 65 C.

After filtration of 17 parts by volume of solution through 1 part byvolume of exchanger resin, the discharge from the column is still freefrom indium whilst the zinc content in the filtrate has increased to 45to 50 mg/l, and it contains an average of2l mg/l.

After the column has been washed, it is eluted with 3N HCl. 1.6 parts byvolume of eluate contain 100 percent In and percent Zn of the originalsolution.

We claim:

1. A process for decreasingthe contaminating metal content of an aqueouscadmium solution having a pH of between 1.5 and 5 and containing atleast one contaminating metal selected from the group consisting oflead, cobalt, zinc, silver, nickel, iron, indium, copper and thallium,said process comprising contacting said aqueous cadmium solution with acation exchange resin having aminocarboxylic acid or iminocarboxylicacid groups as the active exchange. groups and in the form of the alkalimetal, alkaline earth metal, ammonium or cadmium salt thereof andrecovering effluent from said contact step.

2. The process of claim 1 wherein the cation exchange resin, followingsaid contact, is eluted and the eluate is recovered. a

3. The process of claim 1 wherein the carboxylic acid moietyof saidactive exchange groups contains from one to five carbon atoms.

4. The process of claim 1 wherein said cation exchange resin comprises acrosslinked polymer of a monomer having at least one olefinic doublebond, said polymer having said aminocarboxylic or iminocarboxylic groupsthereon as substituents.

5. The process of claim 1 wherein the temperature of

2. The process of claim 1 wherein the cation exchange resin, following said contact, is eluted and the eluate is recovered.
 3. The process of claim 1 wherein the carboxylic acid moiety of said active exchange groups contains from one to five carbon atoms.
 4. The process of claim 1 wherein said cation exchange resin comprises a crosslinked polymer of a monomer having at least one olefinic double bond, said polymer having said aminocarboxylic or iminocarboxylic groups thereon as substituents.
 5. The process of claim 1 wherein the temperature of said aqueous cadmium solution is from 60* to 80*C.
 6. The process of claim 1 wherein each liter of cation exchange resin volume is contacted with from 2 to 25 liters of aqueous cadmium solution per hour.
 7. The process of claim 1 wherein each liter of cation exchange resin volume is contacted with from 4 to 10 liters of aqueous cadmium solution per hour. 